This sort of speed control apparatus as described in Patent literature 1 can automatically drive a vehicle according to a predetermined running speed pattern by controlling an accelerator and brake of the vehicle. Also, an apparatus that is adapted to, in the case of a vehicle having a clutch, such as a manual transmission car, control a position of the clutch to control a speed of the vehicle during a certain period of time from a start has been conventionally known.
To describe specifically, the conventional speed control apparatus moves the clutch from a disconnect position to a predetermined slip position in advance slightly before a starting time point when a commanded vehicle speed rises from zero, and at and after the starting time point, drives the clutch by an amount corresponding to a deviation between the commanded vehicle speed and an actual vehicle speed such that the actual vehicle speed follows the commanded vehicle speed.
The reason why the clutch is moved to the slip position in advance slightly before the starting time point as described is because if feedback control of the clutch is started at the disconnect position, as illustrated in FIG. 1, the clutch starts to move eventually after the deviation between the commanded vehicle speed and the actual vehicle speed has been generated, and therefore a time lag inevitably occurs to deteriorate followability to the commanded vehicle speed at the starting time point.
However, the clutch is moved to the predetermined slip position (hereinafter also referred to as an initial intermediate position) before the starting time point, and therefore in the case where a rising angle of the commanded vehicle speed, i.e., commanded acceleration is small, as illustrated in FIG. 2, a situation where the actual vehicle speed exceeds the commanded vehicle speed may come up at the beginning of the start. This is because in the case of moving the clutch to the slip position, power is transmitted to wheels, and the vehicle attempts to move at a certain level of acceleration.
However, if the slip position is set to a position close to the disconnect position of the clutch, in the case where in turn, the commanded acceleration is large, a situation where the actual vehicle speed cannot sufficiently follow the commanded vehicle speed comes up immediately after the start.
Meanwhile, in order to perform a dynamic running performance test of a vehicle, vehicle running simulation driving has been performed by a chassis dynamometer, and in the running performance test, an automatic vehicle driving apparatus has been used in order to make it possible to perform the test constantly under the same running conditions. The automatic vehicle driving apparatus is configured to be able to automatically perform operations of pushing amounts of an accelerator pedal, clutch pedal, and brake pedal, switching of a shift lever, and other operations with use of actuators such as motors (see Patent literature 2).
More specifically, by referring to a running performance map so as to follow a predetermined running pattern provided for by the running performance test, sequentially required accelerator opening levels are obtained, and to achieve the accelerator opening levels, control of the accelerator pedal is performed by an accelerator opening level control mechanism. Note that the running performance map refers to data in which in learning driving, vehicle speeds and acceleration values are obtained at variously different accelerator opening levels, and the accelerator opening levels, vehicle speeds, and acceleration values at multiple points are related to one another.
Meanwhile, in the running performance test, in addition to making a vehicle speed of a vehicle follow a vehicle speed provided for by regulations, an engine rotation number is also required to keep an appropriate value. For example, at the starting time point of an MT car, it is required to keep an engine rotation number that prevents an engine from stalling due to a variation in connecting amount of a clutch, and also to prevent an engine rotation number higher than necessary from being outputting. This is because in the case where the engine rotation number higher than necessary is outputted, even if the vehicle can follow the running pattern, for example, a test result of analyzing exhaust gas from the vehicle is adversely influenced as compared with the case of an adequate amount of engine rotation number.
In recent years, engine characteristics have been changed, and therefore in vehicle speed control based on an automatic vehicle driving apparatus at the starting time point of an MT car, when the vehicle control is performed with the running performance map being referred to, an engine rotation number tends to have a higher value than an expected value. In order to solve such a problem, an automatic vehicle driving apparatus having an accelerator control system 104 configured for a starting time point as illustrated in FIG. 12 is used in some cases.
The accelerator control system 104 illustrated in FIG. 12 is described. In this diagram, a vehicle VH is an MT car that receives accelerator and clutch operations, and an accelerator opening level control mechanism 5A illustrated in a block immediately before a block of the vehicle VH is a mechanism that receives an accelerator opening level serving as a target value, and changes an accelerator pushing amount so as to achieve the accelerator opening level.
First, in a target vehicle speed generation part 1A, from a vehicle speed pattern Vpat specified by a running pattern, a target vehicle speed Vref to be achieved by the vehicle VH is generated. An accelerator calculating part 2A in a stage subsequent to the target vehicle speed generation part 1A differentiates the target vehicle speed Vref to output target acceleration αref.
A running performance map reference part 4A in a stage subsequent to the acceleration calculating part 2A is inputted with a deviation Vnew between the target vehicle speed Vref and an after-mentioned correcting vehicle speed Vamd, and the target acceleration αref, and refers to the running performance map for the vehicle VH on the basis of such vehicle speeds and acceleration to output each corresponding accelerator opening level θmap. The accelerator opening level control mechanism 5A changes an accelerator pushing amount Aact so as to achieve the accelerator opening level θmap that is outputted with reference to the running performance map.
Note that a vehicle speed correcting part A1 illustrated in the middle of a loop returning from the vehicle VH to the running performance map reference part 4A is a component that is provided in order to prevent the engine rotation number from being made higher than the desired value as described above. The vehicle speed correcting part A1 is placed on the basis of the idea that if the target vehicle speed is decreased by an amount corresponding to a deviation Rerr between the engine rotation number Ract measured in the vehicle VH and a target engine rotation number Rref, the engine rotation number will also be decreased, and one that converts the excess engine rotation number Rerr into a vehicle speed in consideration of a gear ratio, clutch connecting amount, and tire diameter of the vehicle VH to output the above-described correcting vehicle speed Vamd.
The automatic vehicle driving apparatus having the accelerator control system 104 configured for the starting time as illustrated in FIG. 12 outputs the accelerator opening level θmap with reference to a point P2 that is a point lowered in terms of an inputted vehicle speed value from a point P1, which was supposed to be referred to if the vehicle speed correcting part A1 was absent, by an amount equal to the vehicle speed corresponding to the excess engine rotation number Rerr, as illustrated in a graph of FIG. 9. To the extent of seeing the graph of FIG. 9, it is considered that for example, in the case where the engine rotation number is made too high, the accelerator opening level having a target value to be inputted to the accelerator opening level control mechanism 5A is reduced from θ2 to θ3 because of the presence of the vehicle speed correcting part A1, and as a result, the accelerator pushing amount Aact is moved back to decrease the engine rotation number Ract.
However, in practice, as a result of an experiment made by the present inventor, even in the case where the accelerator control system 104 for the starting time was configured as illustrated in FIG. 12, an engine rotation number excessively increased at the starting time of an MT car was unable to be sufficiently decreased and restored to a value close to a desired engine rotation number.
The reasons why even in the case where the accelerator control system 104 as illustrated in FIG. 12 was used, the engine rotation number was unable to be prevented from being excessively increased at the starting time point of the MT car may include the following reasons.
(1) The running performance map is created by collecting pieces of data on accelerator opening levels corresponding to various combinations of a vehicle speed and acceleration; however, measurement for the collection can be made only in a state where a clutch is completely rigidly connected. That is, in a state where the clutch is in the connecting, such as a half-engaged clutch state at a starting time, i.e., in a state where a torque variation easily occurs, the running performance map is fundamentally inaccurate, and even in the case where the running performance map reference part refers to the accelerator opening level at the target vehicle speed obtaining by subtracting the vehicle speed corresponding to the excess engine rotation number as illustrated in a graph of FIG. 13, the accelerator opening level enough to sufficiently decrease the engine rotation number is not necessarily returned. As described, the fact that reliability of the running performance map itself is low in a region where the clutch is not completely connected is considered to be one of the big reasons why the engine rotation number cannot be well controlled.
(2) In addition, a reason other than the accuracy of the running performance map can also be considered. Even if the running performance map in vehicle speed and acceleration regions at the starting time has a certain level of accuracy, it is not that an absolute value of a slope of the acceleration with respect to the vehicle speed under the condition of a constant accelerator opening level is large as illustrated in the graph of FIG. 13, but the absolute value may be substantially horizontal as illustrated in FIG. 14. In the case of a vehicle having such a running performance map, even in the case of referring to an accelerator opening level with subtracting a vehicle speed corresponding to an excess engine rotation number, the accelerator opening level outputted from the running performance map reference part changes little. Accordingly, the accelerator pushing amount from the accelerator opening level control mechanism also changes little, and therefore it is considered that the state where the engine rotation number is high is kept.
Further, at the starting time of the MT car, the engine rotation number is not only excessively increased, but instead, depending on characteristics of an engine, may be excessively decreased to stall the engine. In such a case as well, it is difficult for the accelerator control system as illustrated in FIG. 12 to restore to the desired engine rotation number.